1. Field of the Invention
The present invention relates to a developer device engaging and disengaging mechanism for an image forming apparatus.
2. Description of the Related Art
As use of office automation systems has become widespread in recent years, demand for image forming apparatus which can form varied and quality characters and images on ordinary paper with low noise, has increased. To meet this demand, image forming apparatuses utilizing electrophotography which is also used in copying machines and facsimile equipment, has been widely used. An image forming apparatus which has components divided into replaceable functional units such as a photoconductive drum and a developer device, is desired, so that those functional units can easily be removed and inserted when the life of the photoconductive drum expires or when toner needs to be replenished in the toner hopper of the developer device.
The developer device is typically positioned near the photoconductive drum and is coupled thereto through a gear. Accordingly, in order to easily insert and remove the developer device to and from an image forming apparatus, a mechanism which can properly engage and disengage the developer device in the apparatus, is in great demand.
FIG. 1 is a side view of an electrophotographic recording unit which consists mainly of a laser beam scanner 1, photoconductive drum 2a, cleaner 3, charger 4, developer station 5a, transfer station 6, discharger 7, fuser station 8a, paper transport path 9, paper stacker 11, and paper hoppers 10a and 10b for recording paper of different sizes.
When a print command is issued to the recording unit in a print-ready state with the power turned on and with a heat roller R1 of the fuser station 8a heated up to a predetermined temperature, the recording unit starts a print operation. That is, a sheet of recording paper 12 of a command-designated size is fed onto the paper transport path 9 and transported in the direction of arrow A, toward the photoconductive drum 2a. By this time, the photoconductive drum 2a has been discharged by the discharger 7, cleaned by the cleaner 3 and newly charged by the charger 4.
The laser beam scanner 1 including a laser oscillator, exposes and scans image data-modulated light onto the photoconductive drum 2a to form an electrostatic latent image thereon. The electrostatic latent image formed on the photoconductive drum 2a is developed by toner 52 which is picked up from a toner container 50 and attached to a developing roll 51a. The toner 52 which is composed of ferromagnetic powder, is charged while being mixed and stirred in the toner container 50. Then, the transfer station 6 transfers the toner-developed image to the recording paper 12 fed from the paper hoppers 10a or 10b. The image transferred is fused by the heat roller R1 and a pressure roller R2 in the fuser station 8a. Finally, the recording paper 12 is fed to the stacker 11.
The recording unit has an upper cover 13, which is on the upper side of the paper transport path 9. The upper cover 13 opens backward by swinging about a shaft (see cover supporting shaft 131 in FIG. 4) positioned to the right of the structure illustrated in FIG. 1.
FIG. 2 is a perspective view of developer station 5a which includes guide pins 54a-54d on the lower part of both sides of a housing 53. A handle 55, provided on the upper part of the housing 53, is used to remove the developer station 5a for maintenance or when the toner 52 needs to be changed (e.g., after 4000-6000 sheets of recording paper have been printed). The developer station 5a also has gap rolls 56a and 56b on the ends of the developer roll 51a.
FIG. 3 is a sectional view of a unit frame 14a, showing guide grooves 15a-15d which are provided perpendicularly in the unit frame 14a of the recording unit. The guide grooves 15a-15d each have at their lowermost end, a hooked portion (e.g., 10 mm-long) which turns at a right angle toward the photoconductive drum 2a. The developer station 5a is mounted on the unit frame 14a by inserting the guide pins 54a-54d along the guide grooves 15a-15d.
FIG. 4 is a side view of a developer station engaging and disengaging mechanism of the related art. A leaf spring 16a is coupled at one end to a shaft 17. An arm 18a is connected at one end to the shaft 17, and at the other end to a spring 19. The spring 19 forces upward the arm 18a and a link bar 20a whose lower end contacts the arm 18a. Thus, when the upper cover 13 is closed with the cover-supporting shaft 131 serving as a rotational axis, a protruding portion 130 provided on the back of the upper cover 13, presses down the link bar 20a. The link bar 20a rotates the arm 18a counterclockwise against the elasticity of the spring 19, and the leaf spring 16a swings in the direction of the arrow B, pressing the rear side 5a' of the developer station 5a. Accordingly, the developer station 5a slides in the direction of the arrows shown in FIG. 3 along the hooked portion of the guide grooves 15a-15d to the far end. Thus, the gap rollers 56a and 56b (see FIG. 2) provided at both ends of the developer roll 51a contact the photoconductive drum 2a at both ends so as to position the developer roll 51a at a predetermined distance from the photoconductive drum 2a.
FIG. 5 is a side view of the developer station 5a of the related art in the engaged position. The developer station 5a is provided with a developer gear 57a which transmits a rotational force from a power transmission mechanism 21 to the developer roll 51a and the toner mixer in the toner container 50 (see FIG. 1). The power transmission mechanism 21 consists of a bracket 22a, gears 25a, G1 and G2, motor gear G3, pulleys P1 and P2, belt B1, motor M, tension roller R and spring SP. The bracket 22a is rotatably-coupled to the unit frame 14a (FIG. 3) via an axis 23a. Coaxially-coupled gear 25a and pulley P1 are rotatably-coupled to one end of the bracket 22a. A spring 26a is provided at the other end of the bracket 22a to force the gear 25a to engage the developer gear 57a. Thus, a driving force is transmitted through the gears 25a and 57a to the developer station 5a as it is engaged properly with the recording unit. Accordingly, when the upper cover 13 (FIG. 4) is opened, the spring 19 causes the arm 18a to rotate, and the leaf spring 16a swings in the direction of an arrow C so that the guide pins 54a-54d of the developer station 5a are released from the hooked portions of the guide grooves 15a-15d. As a result, the developer station 5a can be removed from the apparatus using the handle 55. However, gears 25a and 57a tend to remain engaged until the developer station 5a is manually removed from the image forming apparatus.
As described above, in order to smoothly engage or disengage the developer station 5a by sliding it along the hooked portions of the guide grooves 15a-15d, it is necessary that the gear 25a and the developer gear 57a rotate while being engaged with each other, because of a large rotational torque which the gears provide. Accordingly, it is difficult to engage and disengage the developer station smoothly when the developer station is removed from or inserted into an image forming apparatus when maintenance is required.